1. Field of the Invention
This invention relates to the field of drilling apparatus and hand tools, and especially to a device for forming a bore that follows a curve of predetermined radius around a right angle, through a workpiece such as a wooden building stud.
2. Description of the Prior Art
It is normally and routinely necessary when boring a hole in a workpiece to do the boring with a straight and balanced rotating cutting bit. If the bit is unbalanced, or not straight, the eccentric weight tends to whip the drill bit around, stressing the shaft and eventually bending or breaking the bit, the shaft driving the bit such that the bit whirls around uselessly. It is, of course, not possible to drill a curved hole with a straight and rigid bit.
U.S. Pat. No. 3,709,624--Blank discloses a machine for accurately machining curved holes. The device comprises a rotating table upon which a workpiece is set, and a series of gears driving a bit against which the workpiece is advanced. The gears are disposed alternately at right angles to one another for carrying the power from a driven end to the bit end of a curved power-transmitting means. The Blank device is a heavy-duty apparatus, not suitable for use as a hand tool, and is complex due to the plural gears.
U.S. Pat. No. 3,617,143--McKee discloses a device quite similar to that of Blank. In McKee, a workpiece holding table is provided with means for holding a shaft which has been bent around a curved path. A drilling bit mounted on a curved drive means is then applied to bore out the middle of the shaft to form a pipe. This is considered more accurate by McKee than the more traditional method of bending a pipe around a curved surface, which often is characterized by an internal diameter restriction at the bend.
McKee and Blank disclose specialized heavy duty machine tools that are not suitable as general purpose hand tools.
It is often necessary, particularly in running domestic power wires through studs and other framing elements of a construction project, to route wires around a particular path. When installing domestic power wiring, it is frequently necessary for users of straight drill bits to bore a plurality of holes, or to bore larger holes than would be necessary if it was somehow readily possible to drill a smooth hole around right angles. In addition, surface mounted devices, such as switch plates, light fixtures, and the like, are normally served by power lines that run parallel to the wall or ceiling panel in which the fixture is mounted, the power lines making a right angle adjacent the fixture. While it is possible, given sufficient space, to make a tight right angle turn in the power wire, which is moderately flexible, there is a danger of abrading the wire or breaking conductors therein, and abrupt right angle changes in the path of the wire are likely to make it difficult to fish the wire through wall and ceiling spaces.
U.S. Pat. No. 3,016,073--Broussard et al discloses a flexible drill means wherein it is possible to drill a hole for wire fishing and the like through a fire-stop section of a wall. According to this patent, straight sections and curved sections of a flexible tube are led to a drilling bit. The drilling bit, however, is entirely straight, and drills a straight hole, notwithstanding the flexible drive shaft which causes the bit to rotate.
There has been a need for an apparatus to conveniently and inexpensively drill holes around a curved path in a workpiece such as a framing element or a stud, without the need for a large, complex and expensive apparatus. According to the present invention, a flexible drive shaft tracing around slightly more than 90 degrees terminates in a movable drill bit, rotatably supported at the distal end of a right angle bend of shaft or tubing. The shaft or tubing is carried on a chassis which positions the shaft or tubing precisely along the circumference of a circle around an axis of rotation between the chassis and a workpiece-engaging support. As the chassis is advanced around the workpiece, while rotating the drill bit, a curved hole is formed, the curved path being long enough (somewhat over 90 degrees), to allow room for the drill bit to emerge fully from the workpiece.